A Smart Medical Diagnostic Tool using Resistive Sensor Technology
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A Smart Medical Diagnostic Tool using Resistive Sensor Technology K. K. Iyer, A.K. Prasad and P. I. Gouma Department of Materials Science and Engineering, State University of New York, Stony Brook, NY, 11794-2275. ABSTRACT: This paper reports on the development of a smart sensor array consisting of selective gas sensing elements for use in disease diagnosis to monitor signaling gases. These are gases typically found in exhaled human breath that can serve as biomarkers for specific diseases. Utilizing the polymorphic selectivity of semiconducting metal oxides and by employing temperature modulation we have developed a smart gas selective sensor array able to identify and discriminate between isoprene, NOx, alcohols and amines/NH3. The sensing elements are thin films based on the various polymorphs of molybdenum trioxide. A breath analysis system based on our smart sensor array can be used for non-invasive monitoring and differential diagnosis of diseases. INTRODUCTION: Electronic Olfactory Systems (EOS) or E-noses as they are called employ an array of nonselective gas sensors used for recognizing and discriminating complex gas mixtures. In the case of simple mixtures, E-noses are used to quantify the concentration of the constituents. The important parts of an electronic nose are its sensor array, electronic circuitry and data analysis software. The sensing elements can be semiconductor thin films like MOSFETs and metal oxides or organic components like conducting polymers and metalloporphyrins [1, 2]. Such electronic noses that can mimic the human olfactory system have been used predominantly in the food industry for evaluation of food quality [3, 4], for environmental monitoring and more recently in medical applications [5, 6]. The most common problem encountered with these sensor array systems is that they suffer from poor selectivity and hence necessitate the use of complex pattern recognition software for discriminating the gases. Developing solid state sensors with the required selectivity has been a major challenge. When using metal oxide based resistive sensors, their sensitivity to a particular gas can be improved by doping with noble metal elements like Pt [7], Pd [8]. The operation of these sensors at high temperatures leads to the diffusion of these noble metal dopants into the metal oxide matrix over prolonged periods of operation and results in the formation of solid solutions that may lead to a change in the sensor behavior. This may also lead to a drift in the baseline resistance of the sensors and hence could result in erroneous measurements. An ideal method would be to achieve the required selectivity using a single undoped metal oxide system. This paper discusses the use of a solid state gas sensor array that includes various polymorphic phases of the same metal oxide to achieve differentiation among classes of gases. The sensors are thin films of nanostructured molybdenum trioxide. Temperature modulation has also been attempted to improve the sensors’ selectivity to specific gases.
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